Typically, semiconductors devices are formed by epitaxial growing of successive semiconductor layers on substrates, i.e., wafers, using chemical vapor deposition (CVD) processes. In a CVD process, a plurality of wafers which are placed in pockets of a wafer carrier, and which are kept in an elevated temperature, are exposed to precursor gases, and the precursor gases react and are deposited epitaxially on the wafers to form a semiconductor layer. To obtain uniform semiconductor layers of the wafers, considerable effort has been devoted to maintain wafers in uniform conditions. For example, a conventional wafer carrier disclosed in US patent publication no. 2010/0055318. Thus, for evenly treating the wafers on the wafer carrier, in a typical CVD process, the wafer carrier is rotated about its central axis. As the centrifugal force will be generated as a result of rotation of the wafer carrier, each wafer placed on the wafer carrier will unavoidably be forced to engage an inner periphery of a corresponding one of the pockets, thereby resulting in undesirable defects such as slip lines on peripheries of the wafers.